JEE MATHEMATICS MCQ: SEQUENCE OF SERIES

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Let

{a_1},\,\,{a_2},......{a_{21}}

be an AP such that

\sum\limits_{n = 1}^{20} {\frac{1}{{{a_n}{a_{n + 1}}}}} = \frac{4}{9}.

If the sum of this AP is 189, then

{a_6}{a_{16}}

is equal to

View answer and explanation

Correct option: B

Option B (72) is correct because solving the given equations for the arithmetic progression leads to a_6 * a_16 = 72.

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